Conventionally, in viewing an AV appliances and the like, a number of cords are connected to the device for signal transmission. Because of the numbers of cords, there had been problems such as the freedom of placing of the device is narrowed, aesthetic appeal thereof is deteriorated, dust tends to attach thereto, causing a difficulty in cleaning. However, in recent years, a wireless configuration is being widespread in signal transmissions, and it is becoming possible to eliminate the cords for signal transmission by using a wireless configuration.
However, even if the cords for the signal transmission are eliminated by a wireless configuration, a cord for transmitting and receiving electric power still exists; thus, many of the problems related to the thick and long cord remained.
For example, in devices such as a cellular phone, a personal computer, a mobile device and the like that can easily be carried around without any cords, battery-charging is required, so the charging is performed by using an AC adapter to be plugged into a receptacle. Due to this, since a charger cord of the AC adapter extends to the receptacle, aesthetic appeal around the receptacle is deteriorated, and the cord is easily tripped over by a human foot.
Especially in a household, there may be cases in which a large number of cellular phones are charged at one time; in such a case, the number of adapters is increased, and further, aesthetic appeal around the receptacle upon charging is deteriorated, the cords that are intricately tangled are easily tripped over by a human foot, and extra time and effort is needed to untangle the intricately tangled cords.
Further, since an AC adapter is an accessory for the cellular phone, it must be attached to each cellular phone. Due to this, there arise problems that the cost of the cellular phone is increased for the AC adapter, and resources such as copper and the like included in the cord of the AC adapter in a large quantity are exhausted.
In view of such a background, a technique to eliminate a power cord, and to perform contactless, non-contact power supply has been proposed. Especially, in a method using electromagnetic induction (for example, Japanese Patent Application Publication Laid Open (JP-A) No. 2000-325442), its actual implementations as chargers for electric toothbrushes and electric shavers (commercially available since 1998), and cellular phones has started. Further, in the Patent Document 1, a device authentication technique by a signal transmission for authenticating the device to supply power and the like is employed, and the contactless power supply can be provided only to a specific device.
Further, in order to reduce standby power during when a device is not placed, a method to intermittently perform excitation from a primary coil of a power supply apparatus to a secondary coil of the device has also been employed. In some cases, a device may not have an internal power source. Power supply must be periodically performed to confirm that the power source is attached to a device power supply surface, and such a confirmation is performed by using an intermittent oscillation and the like.
However, such a power supply apparatus can only supply power to one device, and cannot supply power simultaneously to other devices, or charge a plurality of devices at one time. Due to this, a plurality of power supply apparatuses is required, whereby cords for the power supply apparatuses are increased, so problems as in the conventional cases rise likewise.
It is an object of the present invention to provide a contactless power supply system capable of simultaneously providing contactless power supply to a plurality of devices, or to different devices.